Bug 1443942 - Block mid-flight redirects to cross origin destinations during media loads. r=jya

There's no compelling use case for mid-flight redirects, and Chrome
already blocks it, so there's little point in maintaining it.

Add a hidden pref to toggle blocking, so we can toggle it off during
testing to ensure that we're blocking a working mid-flight redirect.

MozReview-Commit-ID: EnGNmYFr8Uv

--HG--
extra : rebase_source : cdc122a11a648f2451d2983df42597d8274ac9fb

dom/media/ChannelMediaDecoder.cpp

@@ -166,10 +166,9 @@ ChannelMediaDecoder::NotifyPrincipalChanged()
     mInitialChannelPrincipalKnown = true;
     return;
   }
-  if (!mSameOriginMedia &&
-      DecoderTraits::CrossOriginRedirectsProhibited(ContainerType())) {
-    // For some content types we block mid-flight channel redirects to cross
-    // origin destinations due to security constraints. See bug 1441153.
+  if (!mSameOriginMedia && MediaPrefs::BlockMidflightRedirects()) {
+    // Block mid-flight redirects to non CORS same origin destinations.
+    // See bugs 1441153, 1443942.
     LOG("ChannnelMediaDecoder prohibited cross origin redirect blocked.");
     NetworkError(MediaResult(NS_ERROR_DOM_BAD_URI,
                              "Prohibited cross origin redirect blocked"));

dom/media/DecoderTraits.cpp

@@ -325,11 +325,4 @@ bool DecoderTraits::IsSupportedInVideoDocument(const nsACString& aType)
     false;
 }
 
-/* static */
-bool
-DecoderTraits::CrossOriginRedirectsProhibited(const MediaContainerType& aType)
-{
-  return WaveDecoder::IsSupportedType(aType);
-}
-
 } // namespace mozilla

dom/media/DecoderTraits.h

@@ -57,10 +57,6 @@ public:
   static bool IsMatroskaType(const MediaContainerType& aType);
 
   static bool IsSupportedType(const MediaContainerType& aType);
-
-  // For some content types we block channel redirects to cross origin
-  // destinations due to security constraints. See bug 1441153.
-  static bool CrossOriginRedirectsProhibited(const MediaContainerType& aType);
 };
 
 } // namespace mozilla

dom/media/MediaPrefs.h

@@ -205,6 +205,9 @@ private:
 
   // Media Seamless Looping
   DECL_MEDIA_PREF("media.seamless-looping",                   SeamlessLooping, bool, true);
+
+  DECL_MEDIA_PREF("media.block-midflight-redirects",           BlockMidflightRedirects, bool, true);
+
 public:
   // Manage the singleton:
   static MediaPrefs& GetSingleton();